1. Field of the Invention
The present invention relates to an ultrasonic diagnostic apparatus using an ultrasonic probe of a mechanical radial scanning type for intracavity observation, and relates to a signal processing program to be used in the ultrasonic diagnostic apparatus.
2. Description of a Related Art
In medical fields, various imaging technologies have been developed for observation and diagnoses within an object to be inspected. Especially, ultrasonic imaging for acquiring interior information of the object by transmitting and receiving ultrasonic waves enables image observation in real time and provides no exposure to radiation unlike other medical image technologies such as X-ray photography or RI (radio isotope) scintillation camera. Accordingly, ultrasonic imaging is utilized as an imaging technology at a high level of safety in a wide range of departments including not only the fetal diagnosis in obstetrics, but also gynecology, circulatory system, digestive system, and so on.
The principle of ultrasonic imaging is as follows. Ultrasonic waves are reflected at a boundary between regions having different acoustic impedances such as a boundary between structures within the object. Therefore, by transmitting ultrasonic beams into the object such as a human body, receiving ultrasonic echoes generated within the object, and obtaining reflection points where the ultrasonic echoes are generated and reflection intensity, outlines of structures (e.g., internal organs, diseased tissues, and so on) existing within the object can be extracted.
Further, an ultrasonic endoscope for obtaining ultrasonic diagnostic images by performing scanning within a body cavity by using ultrasonic waves has been conventionally proposed. In the ultrasonic endoscope, an electronic scanning system has been recently proposed against a conventional mechanical scanning system. The electronic scanning system can perform scanning with a higher degree of freedom than the mechanical scanning system and can realize a Doppler mode (including a CF (color flow) mode and a PW (pulse wave) mode) in addition to a B (brightness) mode, and is becoming predominant.
Here, the B-mode refers to a mode of converting amplitudes of ultrasonic echoes into brightness and displaying a two-dimensional tomographic image. Further, the CF mode refers to a mode of mapping average blood flow velocities, flow fluctuation, intensity of flow signals, flow power, or the like in various colors and superimposing it on the B-mode image, and the PW mode refers to a mode of displaying velocities of ultrasonic echo sources detected based on transmission and reception of pulse waves.
Furthermore, as a device similar to the ultrasonic endoscope, there is an ultrasonic probe to be inserted into a forceps hole of the endoscope. However, since the ultrasonic probe has a thin diameter, only the mechanical radial scanning system is realized. In the mechanical radial scanning system, a displayed image often rotates due to uneven rotation (jitter) of a flexible shaft for rotating ultrasonic transducers. Especially, in the Doppler mode, there has been a problem that a displayed image (object) rotates relative to an ROI (region of interest) or a gate position to be set, and a region really desired to be observed is out of a field of view.
As a related technology, Japanese Patent Application Publication JP-P2005-270149A discloses an apparatus that can perform a quantitative image diagnosis within a cardiac blood vessel (coronary vessel) in a short time (in real time) at low cost. The apparatus is an apparatus for obtaining a tomographic image of a blood vessel based on reflected waves (ultrasonic echoes) of an ultrasonic beam radiated from an ultrasonic probe provided in a catheter inserted into the blood vessel, and includes (1) means for irradiating entire circumference of the vessel wall while rotating the ultrasonic probe, observing ultrasonic echoes from the vessel wall, and analyzing a Doppler shift frequency as a difference between a frequency of the irradiating ultrasonic beam and a frequency of the ultrasonic echoes, i.e., an amount of shift change produced due to a Doppler effect, (2) means for removing an influence of movement of the catheter center due to the influence of pulsation by adding a Doppler shift frequency in a certain irradiation direction and a Doppler shift frequency observed in a direction at 180 degrees from that direction to each other in order to remove a Doppler shift frequency depending on the movement of the catheter center from the Doppler shift frequency, and handling only the Doppler shift frequency from the vessel wall, and (3) means for digitizing an ultrasonic frequency by A/D conversion and analyzing it by using a computer image information processing unit in order to compute a tomographic image of the blood vessel based on the Doppler shift frequency by the vessel wall, and displaying a structure of the vessel wall as an image.
That is, JP-P2005-270149A proposes a method of canceling fluctuation of the ultrasonic probe center position when the Doppler shift amount is observed in the Doppler mode. However, the method cannot deal with the case where the observed region rotates.
Further, Japanese Patent Application Publication JP-A-10-248844 discloses an ultrasonic image diagnostic apparatus that can obtain image data without reduction of the field of view of an ultrasonic tomographic image and without rotation of image even when image shift occurs, and thereby, construct an accurate three-dimensional image without distortion. The ultrasonic image diagnostic apparatus includes an ultrasonic probe for obtaining three-dimensional image data including continuous plural ultrasonic tomographic images, rotating means for performing rotation processing on a first ultrasonic tomographic image among the plural ultrasonic tomographic images, and correlation computing means for performing correlation computation of the first ultrasonic tomographic image rotation-processed by the rotating means and a second ultrasonic tomographic image among the plural ultrasonic tomographic images to output a correlation value, wherein the rotating means performs rotation processing again on the first ultrasonic tomographic image by an angle at which the correlation value computed by the correlation computing means is the highest.
The ultrasonic image diagnostic apparatus according to JP-A-10-248844 obtains an amount of rotation from the correlation value of the image data representing continuous plural images in three-dimensional display of a B-mode image, and performs polar coordinate conversion for correcting the angle shift to obtain a corrected three-dimensional image. However, there is no consideration to the Doppler mode requiring real time operation.